If you're feeling down, David "Big Dave" Sylvester wants to help.

"Free high fives, free hugs, anything to make you smile," calls out Sylvester, 53, as he stands in front of Dilworth Park on a brisk Thursday morning.

In between his hands, a sign reads, "Hello, my name is Big Dave. #BigDaveHugsTheWorld," which he shifts to his left hand every time he reaches up to touch palms with those passing by.

Across 30 minutes, dozens of strangers take Sylvester up on his offer, from police officers to suit-clad businesspeople to students hustling from the subway to their next destination. All reach a hand to the sky for a golden smack, occasionally to be followed by a deep embrace in Big Dave's arms.

Over the last 17 years, Sylvester has clasped hands or squeezed arms with what he estimates to be around 250,000 people in 36 countries worldwide. He chronicles his journey on his website and social media, like Instagram where his handle is @thehumanhigh5. "A hug and a high five is something we can all do — it's a moment of power."

Outside of City Hall, that power manifests itself in the form of instant smiles across faces of those of every age. Often isolated into their own worlds, with headphones hanging down from ears to phone, people stop in their tracks to take in the unexpected nature of Sylvester's sign and welcoming vibe. Sometimes, the power generates not only a quick grin, but sudden tears, too.

"I'll get people who come up and hug me and just start crying," says Sylvester. "Often they'll say little else but 'I really needed that' and then keep walking."

Not everyone, of course, wants to interact with Sylvester, and many wonder what’s the point of all that he’s doing. This includes tons of passersby casting skeptical looks and a Center City District (CCD) security guard who not only declines a high five, but eventually kicks Sylvester out of Dilworth Park.

For Sylvester, however, the goal is simple: to enhance the world one interaction at a time. Sylvester launched his continuous hugging and high-fiving mission after he lost a childhood friend on 9/11.

"I felt helpless, and I simply didn't want to feel like that anymore," says Sylvester.

In the aftermath of the terrorist attacks, he noticed a loss of trust and civility within society that he believes has only continued to grow.

"There's this stranger-danger ideology," says Sylvester. "Being a large dude with a sign soliciting hugs makes me an oddity, but a smile is your biggest offense — it disarms people, no matter where you are in the world, and sets the mood to let someone know that you're not trouble."

His mission began on a bike trip in 2002, starting in Washington state and taking Sylvester back to his hometown of Philadelphia. It continued as he later traveled across Africa from Cairo to Cape Town, in Asia from Istanbul to Beijing, in Australia from Sydney to Melbourne, and all across the United States. Last month, Sylvester visited his 50th and final state, Alaska, where he journeyed to six different cities with his #BigDaveHugsTheWorld sign.

As Sylvester sees it, everyone deserves a hug — one of the most basic forms of human contact.

"I'll hug anyone. I've even hugged people wearing Confederate hats, in cities where there aren't many black people, and we had a good moment." says Sylvester. "I'm just trying to open people's minds, even just a little bit. Change doesn't happen overnight, but from one good moment a lot can begin to happen."

And if a hug from a stranger feels just a little too uncomfortable, a high five will still create connection.

"People don't always need that much to hang in there — a simple hug can do a lot," says Sylvester, en route to Parliament Coffee shortly after the CDC security guard incident.

Upon stepping into Parliament, a barista gives him a high five without hesitation before starting on his double-espresso order.

"At first it was unexpected, but it became this sort of personal moment he'd have with all of the baristas — most people don't stop to share a moment like that with you in a job like this," says Yashaswi Dixit, one of three baristas Sylvester high-fives that morning at the cafe. "It gets you out of a stressed headspace, even if only temporarily."

Big Dave is well-known around a handful of coffee shops across the city. Even when he's not carrying his sign, you can find him hugging and high-fiving in most places that he frequents.

"The world is going crazy and I'm just doing what I can to try to stop some of the craziness. We've become more polarized than ever, and we've simply lost sight of connecting with people," says Sylvester. "Black, white, straight, gay, Democrat, or Republican — the power of a hug and a high five doesn't discriminate."

Among his journeys, Sylvester makes it a point to visit places touched by violence, like San Bernardino, Calif., after the 2015 mass shooting; Sutherland Springs, Texas, after the church shooting in 2017; and Benton, Ky., after the Marshall County High School shooting earlier this year.

"Initially people are staring at you, and they're wondering what's the catch. But then when people see that you're genuinely there just to hug and high-five, you can see their shoulders soften," says Sylvester. "I'm there to listen if they need me, and give people a relief from cynicism."

Sylvester says he himself has been blessed by kindness from the many people he's met through the experience, including from those he serves at his current job.

"I'm fortunate to work a job where I set my own schedule, but I'm not rich," says Sylvester, a personal trainer at the Union League. "I've had very supportive clients who help with airfare for trips, like to Orlando, after the Pulse nightclub shooting. They get behind the power of what my story is doing to help people and encourage me to keep pushing on."

There are times on trips where Sylvester spends the night in his car, not willing to let financial issues stop him from going out and delivering hugs.

Other challenges include dealing with hecklers, which Sylvester notes makes it essential to possess the ability to laugh things off and keep on moving.

"Hugging people that smell or are dirty is just another hazard of the job," says Sylvester.

He'll often carry two or three of the exact same outfits on his trips so that he can quickly change in his car if needed, and return to the streets without offending anyone. "A lot of those people are really sweet and some of the best huggers," says Sylvester of some of the stinkier situations he's encountered.

Not one to turn his nose up at anyone, his openness doesn't go unnoticed.

“His vulnerability, it’s contagious,” says Shiva Wheeler, randomly stopping to hug Big Dave after crossing paths en route to the Barnes Foundation. “He’s spreading the love, and I wish more people would do that.”